Ligand Controls the Activity of Light-Driven Water Oxidation Catalyzed by Nickel(II) Porphyrin Complexes in Neutral Homogeneous Aqueous Solutions.

ABSTRACT: Finding photostable, first-row transition metal-based molecular systems for photocatalytic water oxidation is a step towards sustainable solar fuel production. Herein, we discovered that nickel(II) hydrophilic porphyrins are molecular catalysts for photocatalytic water oxidation in neutral to acidic aqueous solutions using [Ru(bpy)₃ ]²⁺ as photosensitizer and [S₂ O₈ ]^2- as sacrificial electron acceptor. Electron-poorer Ni-porphyrins bearing 8 fluorine or 4 methylpyridinium substituents as electron-poorer porphyrins afforded 6-fold higher turnover frequencies (TOFs; ca. 0.65 min^-1 ) than electron-richer analogues. However, the electron-poorest Ni-porphyrin bearing 16 fluorine substituents was photocatalytically inactive under such conditions, because the potential at which catalytic O₂ evolution starts was too high (+1.23 V vs. NHE) to be driven by the photochemically generated [Ru(bpy)₃ ]³⁺ . Critically, these Ni-porphyrin catalysts showed excellent stability in photocatalytic conditions, as a second photocatalytic run replenished with a new dose of photosensitizer, afforded only 1-3 % less O₂ than during the first photocatalytic run.

SUBMITTER: Liu C 

PROVIDER: S-EPMC8252617 | biostudies-literature | 2021 Jun

REPOSITORIES: biostudies-literature